1. Field of the Invention
The present invention relates to a polypropylene resin composition with improved weather resistance, and to moldings of films and sheets comprising the composition. Precisely, it relates to a polypropylene resin composition which colors little (in pale red) even when exposed to relatively high temperatures while stored indoors, and to moldings of films and sheets comprising the composition.
2. Description of the Related Art
Polypropylene resins are known to be degraded by various factors in the environment, such as sunlight, atmospheric temperature, oxygen in air, etc. Various weatherproofing agents are added to polypropylene resins so as to retard the degradation of the resins.
However, even though ordinary weatherproofing agents are added to polypropylene resins, the moldings of films and sheets comprising the resulting resin composition often color in pale red on their surfaces in a few months if they are exposed to relatively high temperatures while they are stored indoors.
The reason for such coloration is not clear. However, it is said that the coloration is not caused by the degradation of the polymer itself but is by the additives which color by themselves, and, in experiences, it is known that the degree of coloration depends on the type of the additives. At present, therefore, phenolic antioxidants which color in a lower degree are being used for polypropylene resins, in place of amine-based antioxidants which color in a higher degree.
However, even polypropylene resin compositions comprising such a phenolic antioxidant are still not on a satisfactory level.
With no effective measures for solving the problem, polypropylene resins have heretofore been used exclusively in the field in which the coloration could be negligible. Recently, however, films of polypropylene resins as degraded with organic peroxides are being put into practical use, and their coloration is now being a serious problem in the art.
Given that situation, the object of the invention is to provide moldings of films and sheets of polypropylene resins which color little even when stored indoors at relatively high temperatures, and to provide a polypropylene resin composition useful as the starting material for the moldings.